Thermostat is completely blank or dead, no display

Safety first: Turn off power to the furnace/air handler at the breaker before removing panels or touching wiring.

Steps to troubleshoot:

• 1. Check other equipment: See if the furnace or air handler status lights are on. If not, the unit may have no power.
• 2. Verify breaker and switch: Ensure the HVAC breaker and any service switch near the furnace are ON.
• 3. Inspect thermostat wiring: Remove the thermostat and confirm R and C wires are firmly connected and not corroded or broken.
• 4. Check furnace fuse: Open the furnace access panel and inspect the low-voltage fuse on the control board. Replace with the same rating if blown.
• 5. Test with batteries (if supported): Install fresh batteries in the thermostat. If the display returns, the C wire or transformer may be faulty.
• 6. Test with spare thermostat: If available, connect a basic thermostat to verify that 24VAC is present and the system powers it.

When to call a professional: If there is no 24VAC at the furnace board or fuses keep blowing, contact an HVAC technician to diagnose transformer or wiring faults.